1. Field of Invention
The present invention relates to a projecting apparatus and, in particular, to a solid rod dust-proof structure for projecting apparatuses.
2. Related Art
Shown in FIG. 1 is a schematic view of an optical system of a projecting apparatus. The apparatus includes a reflection mirror 10, a light source 11, a first lens set 12, a solid rod 13, a second lens set 14, a projecting display apparatus 15, an image formation device 16 and a display screen 17. The first lens set 12 consists of at least a lens. The solid rod 13 being an optical device that can homogenize the light passing through includes an incident-beam surface 131 and an outgoing-beam surface 132. The second lens set 14 consists of at least one lens or optical device. The projecting display apparatus 15 can be a transmissive LCD, a reflective LCD, a digital micro device (hereinafter as DMD) or other display devices.
The projecting display apparatus 15 in FIG. 1 is a transmissive LCD and the image formation device 16 is a projecting device. Through the solid rod 13, light can be converged onto the incident-beam surface 131 of the solid rod 13 by directly transmitting from the light source 11 or by reflecting from the reflection mirror 10 and through the first lens set 12. The light that is homogenized after passing through the solid rod 13 reaches the projecting display apparatus 15 through the second lens set 14. Therefore, the image on the projecting display apparatus is projected onto the display screen 17 by the image formation device 16.
The projecting display apparatus 15 in FIG. 2 is a DMD. The light, transmitting to the DMD 15 and being reflected from the DMD 15 to the image formation device 16, projects the image formed on the DMD 15 toward the display screen 17. image formed on the DMD 15 toward the display screen 17.
The projecting display apparatus 15 in FIG. 3 is a reflective LCD. When light enters the second lens set 14, it first transmits to the projecting display device 15, reflects back on the second lens set 14. Afterward, the light, turning a 90-degree angle and transmitting to the image formation device 16 projects the image formed on the reflective LCD 15 toward the display screen 17.
The main function of the solid rod 13 is to homogenize the light passing through so as to achieve the effect of making the projected image uniform. However, one problem is that: when there is dust on the outgoing-beam surface 132 of the solid rod, the dust will also be projected onto the display screen 17 and to blur the image.
Currently, only the dust on the outgoing-beam surface 132 of the solid rod 13 will be projected onto the display screen 17 while the dust on the other portion will not. Thus, this problem can be solved once a dust-proof structure is provided for the outgoing-beam surface 13.
It is one of the object of the invention to provide a solid rod dust-proof structure for projecting apparatuses that can prevent the outgoing-beam surface of the solid rod from dust accumulation so that the transmitting light through the outgoing plane will not be blocked. This structure can thus avoid the influence of the dust on the projected image.
To achieve the above object, the solid rod in the structure has an incident-beam surface and an outgoing-beam surface. The dust-proof structure includes a housing having a first chamber and a second chamber wherein the cross section of the second chamber is greater than that of the first chamber. The first chamber contains the solid rod, and the opposite end of the second chamber includes a stopping portion for stopping the solid rod. Also, a dust proof plate which is a transparent plate is contained in the second chamber of the housing for completely covering the outgoing-beam surface of the solid rod.
Using the above structure, the outgoing-beam surface of the solid rod can be completely covered by the transparent dust-proof plate so that the structure is free from dust and the light transmitting through the outgoing-beam surface will not be blocked.